As an alternative to Public Switched Telephone Network (PSTN) systems, cellular phone networks have proliferated over the last decades, where users with cellular phones have access to one or more networks at almost any location. Also a recent development is the wide spread use of Voice over IP (VoIP) telephony, which uses internet protocol (IP) over wired and wireless networks. With the availability of such diverse types of communication networks and devices capable of taking advantage of various features of these networks, enhanced communication systems bring different communication networks together providing until now unavailable functionality such as combining various modes of communication (e.g. instant messaging, voice/video communications, data/application sharing, white-boarding, and other forms of communication may be combined with presence and availability information of subscribers).
This technology is also referred to as Unified Communications (UC). A network of servers manages end devices capable of handling a wide range of functionality and communication while facilitating communications between the more modern unified communication network devices and other networks (e.g. PSTN, cellular, etc.). In addition to providing subscribers with the enhanced capabilities such as providing instructions to callers for various status, categories, alternate contacts, calendar information, and comparable features, some UC systems may include collaboration features enabling users to share and collaborate in creating and modifying various types of documents and content may be integrated with malts-modal communication systems providing different kinds of communication and collaboration capabilities. Such, integrated systems are sometimes referred to as Unified Communication and Collaboration (UC&C) systems.
Enhanced communication systems providing multi-modal communications operate in a similar fashion to (sometimes the same) data exchange networks where designated servers and their backups provide services (e.g. routing of calls). Session Initiation Protocol (SIP) is a commonly used communication protocol between components of such systems. Communication between end devices is also facilitated increasingly using wireless networks including, but not limited to, Wireless Local Area Networks (WLANs), Wide Area Networks (WANs), and cellular networks. With, the increase in usage of real-time collaboration such as audio, video, and application sharing, the burden on wireless networks is raised. Enterprise-grade Unified Communication is typically associated with high Quality of Service (QoS) including the assignment of proper bandwidth for voice and video. Bandwidth prioritization creates a challenge for service providers to guarantee multi-modal communication service to their customers when the only connection, available is Wireless WAN (WWAN) such as 3G or 4G networks.